A drug used to treat melanoma that has spread to other parts of the body or that cannot be removed by surgery. It is also being studied in the treatment of other types of cancer. Ipilimumab binds to a substance called CTLA-4, which is found on the surface of T cells (a type of white blood cell). Ipilimumab may block CTLA-4 and help the immune system kill cancer cells. It is a type of monoclonal antibody. Also called MDX-010 and Yervoy.